Youth violence imposes enormous costs on individuals and society. Youth violence is the second leading cause of death among individuals ages 10 to 24. Each year, over 720,000 youth are treated in emergency rooms for violence-related injuries (CDC, 2008a). These harms are particularly acute among minority youth. Improving school environments may serve as an effective preventative intervention because they are environmental anchors for youth and are part of the larger set of structural features of local environments linked to the prevalence of youth violence. Given that most individuals initiate violent behaviors during school years, schools provide a natural nexus in considering how to promote pro-social change within individuals and consequently reduce the prevalence of violence. Outside of the family, schools represent the most important institution of social control. Youth attending poorly-managed and resource-deprived schools are more likely to be exposed to violence, even after accounting for local community and family-related attributes. The concentration of youth on/around school grounds during the most crime prone times of the day, suggests that schools are natural ecological environments from which violence can generate. The proposed study will expand our understanding of the epidemiology of youth violence by analyzing the role of the school as a mediating protective factor. We theorize that improving the school environment is an important mediating factor in reducing aggregate rates of youth violence and victimization. Improving school environments can also putatively foster changing systemic aspects of communities linked to youth violence (e.g., disorder, social cohesion, collective efficacy). Given the lack of experimental evidence, we rely on natural experiments to generate exogenous variation in school environments and assess their effects on youth violence at multiple levels including state, districts, and schools. This approach is commonly used to estimate a causal impact on academic achievement, but has not been applied widely to youth violence outcomes. Our methodology relies on within-state, within-district and within- school variation via fixed effects regressions and, where relevant, instrumental variables and propensity score approaches to estimate the effects on youth violence. We will also disaggregate our estimates by race/ethnicity. The study will be among the first efforts to assess the effects of broad-based social policy efforts aimed at improving school environments on youth violence outcomes at state, district, and school levels. Through the analysis of surveillance data on youth violence and victimization outcomes collected by school districts, law enforcement, and public health departments, we can provide an epidemiological assessment of school effects on youth violence in the community. This project addresses the goals of Healthy People 2010 focus areas of Injury and Violence Prevention. Youth violence imposes enormous costs on individuals and society and its harms are particularly acute among minority populations. The proposed study will expand our understanding of the epidemiology of youth violence by analyzing the role of the school as a mediating protective factor in reducing these harms. This project addresses the goals of Healthy People 2010 focus areas of Injury and Violence Prevention and the National Institutes of Health call for research on racial/ethnic disparities in health.